Boxwoods are susceptible to several parasitic nematodes
(microscopic round worms), including the Southern root-knot nematode (Meloidogyne
incognita), the ring nematode (Mesocriconema), the lesion nematode (Pratylenchus),
and the stunt nematode (Tylenchorhynchus).
Symptoms consist of leaf bronzing, stunted growth and general
decline of boxwood. The microscopic worms feed on the roots, which soon die and
the plant forms lateral roots above the invaded area. These lateral roots in
turn are infested. Repeated infestations and lateral root production result in
a stunted root system resembling a witches` broom.
The life of infested plants may
be prolonged by providing good care (fertilization, mulching) and by watering
the plants thoroughly during dry spells. American boxwood (B. sempervirens)
is resistant to root-knot nematodes and tolerant to stunt nematodes. Nematodes
cannot be totally eliminated from the landscape. The goal is to keep the
population low enough to prevent damaging symptoms that weaken the plant.
Boxwoods should not be grown in soils heavily infested with nematodes. Growing
plants that are not affected by nematodes (grasses, marigolds) will reduce
nematode populations in the long term.
Nematode-tolerant shrubs such as yaupon holly and Burford holly
can be used to replace boxwoods, which were killed by nematodes.